A NASA-led team of astronomers will travel around
the globe this weekend to monitor the 2001 Leonid meteor storm.
Catch their reports live on the web!

November
15, 2001: "[It was] the worst blow ever suffered by
astronomy in the eyes of the public." So wrote astronomer
Charles Olivier after the Leonid meteor shower of 1899.

Olivier's colleagues had predicted a furious meteor storm
that year -- and millions of sky watchers were paying attention.
Even folks normally indifferent to the heavens were outdoors
when the storm was due to erupt. But they saw little. The 1899
Leonids were a conspicuous dud, revealing only how poorly astronomers
of the day were able to forecast meteor activity.

Above: Meteors seem to fill the Little Dipper in this
1966 image of a Leonid meteor storm captured by A. Scott
Murrell. Like most Leonid storms, this outburst surprised sky
watchers.

Now ... fast forward 100 years.

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In 1999 astronomers were once again forecasting a Leonid
meteor storm, but this time they would not be embarrassed. Thousands
of shooting stars appeared over Europe and the Middle East --
right on schedule. Onlookers were amazed as the
storm crested on Nov. 18th within 5 minutes of its predicted
maximum!

Times, it seemed, had changed.

"Leonid forecasts have really improved in recent years,"
says Bill Cooke of the NASA Marshall Space Flight Center. Using
computers to model the orbits of comet trails, "we can now
say with confidence in which years Earth will pass through the
clouds of comet dust that cause Leonid outbursts."

These modern forecasts aren't perfect, though. This year is
a good example: Four independent teams each using computer-aided
methods have issued Leonid predictions. They all agree that storm-level
activity will erupt on Nov. 18th. But they differ on basic questions
such as When?Where? and How big?

Above: Colored curves distinguish Leonid
forecasts by four groups of experts. Why do their results
differ? They all use computers to model the orbits of comet dust
clouds -- but the models contain different data and somewhat
different physics. For instance, Brown and Cooke assigned little
weight to Leonid meteor counts reported in the 19th century,
while others relied substantially on such data. The assumed velocity
of dust grains ejected from the comet can vary from model to
model, as do assumptions about the effect of solar radiation
pressure on the orbits of dust clouds, and the size of the clouds
themselves. Which assumptions are correct? Perhaps the 2001 Leonids
will tell us.

"According to our model, people in Hawaii should see
the greatest number of meteors: one thousand or so per hour,
weather permitting," says Cooke, who works in collaboration
with Peter Brown of the University of Western Ontario. Other
forecasters expect outbursts elsewhere: over North America or
east Asia. Meteor rates there, they say, could climb as high
as 4000 to 8000 per hour. [observing
tips]

To
find out who's right, Cooke and a team of 20 scientists led by
Rob Suggs of the MSFC Engineering Directorate, will spread out
around the world on November 17, 18 and 19 to monitor the shower.
They plan to count Leonids from six locations: Huntsville, Alabama;
Eglin Air Force Base, Florida; Maui, Hawaii; Sunspot, New Mexico;
the U.S. Territory of Guam, and the Gobi Desert in Mongolia.

"We chose these places," explains Suggs, "based
on weather and meteor forecasts." They are all likely to
have clear skies on Nov. 18th, and each site is favored for at
least one of the predicted outbursts.

Above: NASA scientists will monitor the 2001 Leonids
from the Maui Space Surveillance Site atop the 10,000 ft Haleakala
summit.

The scientists, mostly from NASA, the University of Western
Ontario, and the U.S. Air Force, will split into six groups of
3 or 4 observers. "Our teams (except the ones on islands)
will be mobile. They can move away from bad weather if necessary,"
says Suggs. Once they find a clear spot, they will set up low-light
video cameras that can detect stars as dim as 8th magnitude --
about six times fainter than what the human eye can see.

Every hour they will transmit their meteor counts to the Leonid
Environment Operations Center (LEOC) at the Marshall Space Flight
Center. The same data will appear in near-real time on SpaceWeather.com,
so anyone with an Internet connection can monitor the global
storm.

Below: One of the NASA observing sites will be in the
Gobi desert, near Ulaanbaatar, Mongolia. Poor communications
could delay reports from this remote spot until long after the
storm is over.

"Our goal is to distinguish between the various Leonid
forecasts," says Suggs. "By comparing the predictions
to the actual meteor counts, we are laying the groundwork to
improve forecasts in the future."

Better predictions will not only please stargazers, but also
help NASA safeguard Earth-orbiting satellites and spacecraft.
Suggs explains: "If we can tell a satellite operator when
a meteoroid stream is nearby, they can take timely precautions
-- like pointing sensitive hardware away from the incoming space
dust."

Space dust looks harmless enough: Typical grains span just
a few tenths of a millimeter and weigh less than 10-4
grams. But they move very quickly. Leonid meteoroids are faster
than 70 km/s or 157,000 mph. When such a meteoroid hits a satellite
-- like a bullet -- the entire meteoroid is usually vaporized
along with a tiny bit of the satellite itself. Electrons and
ions in those vapors can electrify sensitive components, scrambling
software and triggering mistaken control procedures.

Below: This artist's concept of the "plasma effect"
illustrates how a meteoroid impact can produce electrified vapors
that disrupt spacecraft systems. [more]

The danger to individual spacecraft during the coming meteor
storm will be slight, notes Cooke. A satellite in low-Earth orbit,
for example, would have to span an enormous area -- nearly a
square kilometer -- just to intercept a few Leonid meteoroids.

But there are hundreds of active Earth-orbiting satellites.
"When you add them all together the odds of somebody's satellite
being hit are about 1% to 5%. That's substantial," says
Cooke. "We'll see if anyone is unlucky this year."

Even if satellites escape the Leonids of 2001 unscathed, future
storms will surely pose new threats to space-property. Accurate
predictions could come in handy.... Just ask any 19th century
astronomer: a good meteor forecast can save plenty of embarrassment!

Tune in to SpaceWeather.com
on Nov. 18th and see for yourself which of the 2001 Leonid forecasts
fares best. Meteor counts will appear hourly from around the
world. Among the NASA monitoring sites only the Gobi desert will
likely be omitted because of poor communications with that remote
outpost.

Web Links

Jaw-Dropping
Leonids
- (Science@NASA) Don't rely on NASA astronomers to watch the
Leonids for you. Go outside and see them for yourself!